Effect of C:N:P stoichiometry on soil nitrous oxide emission and nitrogen retention

Abstract

Background: Incorporating high organic carbon amendments (HCA) in the soil can promote microbial nitrogen (N) immobilization. HCA incorporation is thought to reduce N loss via nitrate (NO3−); however, it often increases nitrous oxide (N2O) emissions in upland soils. Aims: We aimed to investigate N2O emission and soil N retention in different soils after co-application of mineral N fertilizer, HCA, and phosphorus (P) fertilizer for alleviating potential microbial P limitation. Methods: We conducted a 42-day incubation experiment with nutrient-rich silty soil (RUS), nutrient-rich sandy soil (RSS), and nutrient-poor silty soil (PUS). Soils were amended with wheat straw, leonardite or sawdust, with 50 mg N kg–1 soil dry weight (dw) and additionally with 0, 140, or 250 mg P kg–1 soil dw. Results: The addition of 250 mg P kg–1 significantly increased CO2 emission by 88.6% and 19.8% in wheat straw-amended PUS and RUS, respectively. In the nutrient-rich soils, HCA co-applied with P mostly did not reduce N2O emissions. In the sandy soil, sawdust and leonardite with 140 mg P kg–1 significantly reduced the cumulative N2O emissions by 76.3% and 76.8%, respectively. In the silty soils amended with wheat straw, the retention of N in the form of microbial biomass and ammonium in soil was paralleled by significantly lower NO3− concentrations. Conclusions: We conclude that P co-application with HCA, such as wheat straw, might improve N retention, even if N2O emissions did not decline. However, we also found that different soils respond very differently to combined HCA, N and P addition, which calls for further research into the underlying mechanisms.